Need to Check Rotary Valve Clearance if Installing NEW Valve and Cover?

[etemplet]

I hope he remachined the O-Ring Groove the exact amount he machined off the face.

From my research, the larger the needle and seat, the lower the pop off pressure. From my experience, pop off is just a number. You set it where you want to get what you need from the carb. I can say this... the higher the pop off setting, the higher the pressure at which the needle reseats. Hence... less leakage. I'm gonna hold my pop off settings to around 30psi. It's right in the middle and the 580 and 787 engines seem to respond better right off idle and no flooding issues when closing the throttle at High RPM. They are perkier.

 

[79MKII]

Here's the latest: Used solder method to check RV clearance and it's .018" to .019". The spec is .010" to .014", so I'm pretty sure that's my starting problem. Additionally, the rv and cover are grooved pretty badly. I purchased a new cover, a new rv and gasket kit from SBT. Installing the new parts, the clearance is measuring .016"! The new rotary valve measures the same and the old at .023". One possibility is that the case is worn. Another is that the machined cover is out of spec.

I contacted SBT explained the situation and asked if there was a tolerance in there machining process.....maybe I needed one on the upper or lower end of it to meet the clearance spec. on my engine. I was told that every cover is machined exactly the same on a brand new cnc with the exact same program. OK, but there are still slight variances from cover to cover and there could certainly have been an error made. The other thing that has me concerned is that the oil grooves are completely machined away on one side only....not sure if that means the part wasn't flat or if that's normal. I was told the grooves don't matter.

Even more concerning....I was told that the solder method isn't really accurate because the lead content has changed over the years. Has anybody ever heard of that? To begin with, the solder I'm using is 30 years old, and secondly, it will only crush as far as the cover will allow....and it won't expand after removing it. It has to be accurate regardless of lead content, no??

 

[79MKII]

As bad as the valve and cover look, is it worth assembling everything and trying it even with the clearance measurement of .016"? I'm sure there will be no returns after running the cover.

 

[mikidymac]

I would be suspect of that cover from SBT too. It sure looks like it wasn't flat in their fixture when they machined it. I can't see any reason they would cut more off the bottom that the top when it should be machined perfectly flat. I think I would return it and order another one. if it was me.

 

[AKnarrowback]

That machined RV cover does not look right at all. Send it back.

 

[79MKII]

Well, after speaking with SBT again, they assured me the cover would be fine. I actually measured everything myself and it all looked good. I installed it and tried it out tonight, it ran great and immediately restarted every time. What a difference!

Back to the original topic of this thread, it's always a good idea to check the RV clearance even with all new parts. In theory, it should be in spec, but if the cases are worn, the gap will vary. In my case some spots are out of tolerance by .001" - .002" but most were right around the upper end at .014" Bottom line is, the old cover and valve were totally shot and even though the case is worn a bit causing a slightly larger gap, it still runs great.

 

[mikidymac]

Well I wouldn’t trust anything SBT says and wouldn’t run it on my ski but we wish you the best and keep us updated.

 

[79MKII]

Well I wouldn’t trust anything SBT says and wouldn’t run it on my ski but we wish you the best and keep us updated.

It worked great.....everything is fixed. The cover and valve from SBT work very well.

Thanks for all the comments everyone!

 

[79MKII]

Oh, I also want to throw this primer system in the garbage and go back to the factory choke setup. I will start another thread on that.....I'll be looking for parts.

 

[etemplet]

If you think about the machining of the rotary valve cover, the outside only fits "air" as in "nothing". What matters is the valve surfaces are machined together and they are all the correct depth. I don't remember my RV cover having grooves. I need to take pictures.